Study Design Bleg

I'm interested in the question of whether there are appreciable differences in the quality of parenting received by adopted children and children raised by their biological parents. Obviously this is an empirical question, so before I commit to any empirical investigation I want to be as confident as possible that a potential investigation would really be measuring what I hope to measure.

The standard way to answer questions about the effects of parenting and genes is through twin studies, which compare the achievement and variance thereof between identical twins raised by different families. It's not hard to think of set-ups of such studies which would allow us to test the hypothesis that there are indeed differences in the quality of parenting given to biological and adopted children; however, I'm struggling to think of set-ups that are actually likely to exist in sizeable numbers. Are there really likely to be many cases, for example, of pairs of identical twins where each set of parents raised one member of each set of twins?

The best design that I've so far been able to come up with and subsequently remember long enough to write down is to compare the achievement of children adopted by extended family with that of children adopted by non-relatives. If there is a biological dimension to whatever causes good parenting, we should expect it to be at least somewhat present when raising nephews, nieces, and grandchildren. Unfortunately there's a confound, in that having extended family who are willing and able to adopt your children is itself a fairly good indicator, so we may end up measuring things other than parenting quality.

Any ideas on other study designs or for improvements?

Diminishing Marginal Returns is not known A Priori

Taken from an online discussion of Austrian economics, in which someone is attempting to prove that the law of diminishing marginal returns can be known a priori.

The law of marginal utility is indeed universally true. Any person will value less of a good more than if he had large quantities of it. For instance, the cigarette addict will value his last two cigarettes higher than if he had all twenty in his pack. He would also value two cigarettes far less if he had a whole carton of them at his disposal. Of course he would prefer to have more of them, which is your point and actually a consequence of the law. The law of marginal utility states that with an increase in quantity, the value of each individual item decreases. Thus, he can put each one to its next best use: 

A.) Smoking one now.
B.) Smoking one in an hour.
C.) Magic tricks with a cigarette.
D.) Having a cigarette for a friend.
E.) Smoking one in two hours.
...

Or, if he's down to his last two, all other uses will be put aside so that he will prefer to smoke one now and the other in an hour, instead of using one for a magic trick, saving one for a friend, etc. The reason he would want more is so that he could achieve all of his desired ends.

Counterexample: suppose your friend will be visiting in an hour and you would like to smoke with him. If you have two cigarettes, you hold onto them so that in an hour each of you will smoke one. If you have only one cigarette, you prefer to smoke it immediately.

Thus, we have a case where your preferred use for your first cigarette is different across the cases where you have differing numbers of cigarettes. Hence, a possible counterexample to the law of diminishing marginal returns, meaning that it cannot be known a priori.

I'm not familiar enough with Austrian economics to know if this is the argument that Mises would use to "prove" diminishing marginal returns, but in any case this argument is bunkum.

(Neoclassical economists have a far better way of establishing the law of diminishing marginal returns: we simply assume it. But at least we're honest about the fact that we're assuming it and have the tools to relax that assumption if necessary. Fortunately it seems to hold up pretty well in the real world).

Greed vs. Self-interest

A lot of people who attack mainstream economics will say it assumes that people are always greedy, and that this isn't the case, therefore it is based upon false premises. I feel like this is unfair - I wouldn't describe "economists believe everyone is always greedy" as a strawman, but it's an unfair way of putting it.

Economists tend to assume people are self-interested. I'm not certain how to cash out the difference between being "greedy" and being "self-interested", but I'm fairly certain there is one. For example, I would much rather eat a nice meal than be poked in the eye. Given a choice between the two, I would choose the meal. I don't think that makes me greedy, but it is definitely a self-interested choice.

Perhaps we might say that being "greedy" implies a certain lack of concern for others. There are people who I care about deeply, and I would say that their well-being contributes to my well-being. Hence, if I had to option to provide a benefit to my brother at minimal material or temporal cost to myself, I would be likely to provide this benefit. We can conceive of this as being self-interested, but it seems weird to describe it as greedy.

Alternatively, perhaps we think of greed as being overly concerned with material wealth, as compared to other valuable things. If someone were to pave over a beautiful garden in order to build houses, I can imagine them being described as a "greedy developer".

In any case, I don't think either of these words - at least as used in the most conventional sense - is really an appropriate way of describing the way economists conceive of self-interest. It's true that our models frequently exclude charitable spending and gifts to other agents, but if you want to call failing to give to charity greedy then (while I agree with you) you're going to have a hard time arguing that people aren't basically greedy, given the rather small size of charitable donations. (And also given that Effective Altruism is seen as radical and unusual. Since I heard of it, EA has always seemed rather obviously correct - at least, so long as one accepts moral realism - and yet, EA evangelism is not just a matter of explaining the basic ideas to people, you generally have to convince them over weeks and months. This strongly suggests to me that, when people donate to charity, the extent to which they help people is not generally at the forefront of their mind.)

Perhaps the best way of explaining the way most people understand the word "greedy" is that it should be viewed as relative to a socially agreed baseline. So it's "greedy" not to pay taxes, and moreover, "paying one's taxes" is defined relative to the intent rather than the letter of the law. (This "intent" can be very nebulous, of course - what is one person's "incentive to promote valuable business and job creation" is another person's "corporate loophole"). But since most people don't really give to charity, it's not greedy not to give - just so long as you do give when everyone is doing so (e.g. school non-uniform day, a leaving present for someone at the office, icebucket challenge).

This is not to say that the assumption that people act "rationally" in the economist's sense is entirely warranted: merely that to suggest it has too low a picture of humans is quite the wrong way to go about attacking it. A far better attack - one which, in my view, has a lot of truth to it - is that it overestimates people. People do not generally set out purposefully so as to best achieve their goals. Indeed, they make certain consistent and predictable errors. This is indeed something of a challenge to the axioms of neoclassical economics - although, with a better awareness of human psychology, it may well be possible to repair the faulty assumptions to make better predictions.